1. Field of the Invention
The invention relates generally to the field of marine geophysical surveying. More particularly, the invention relates to methods for optimizing operating efficiency of marine surveying while maintaining safe tension levels in a towed sensor array.
2. Background Art
Marine geophysical surveying systems such as seismic acquisition systems and electromagnetic survey systems are used to acquire geophysical data from formations disposed below the bottom of a body of water, such as a lake or the ocean. Marine seismic surveying systems, for example, typically include a seismic survey vessel having onboard navigation, seismic energy source control, and geophysical data recording equipment. The seismic survey vessel is typically configured to tow one, or more typically a plurality of laterally spaced apart sensor streamers through the water. At selected times, the seismic energy source control equipment causes one or more seismic energy sources (which may be towed in the water by the seismic vessel or by another vessel) to actuate. Signals generated by various sensors on the one or more streamers in response to detected seismic energy are ultimately conducted to the recording equipment. A record with respect to time is made in the recording system of the signals generated by each sensor (or groups of such sensors). The recorded signals are later interpreted to infer the structure and composition of the formations below the bottom of the body of water. Corresponding components for inducing electromagnetic fields and detecting electromagnetic phenomena originating in the subsurface in response to such imparted fields may be used in marine electromagnetic geophysical survey systems.
The one or more sensor streamers are in the most general sense long cables that have geophysical sensors disposed at spaced apart positions along the length of the cables. A typical streamer can extend behind the geophysical survey vessel for several kilometers. Because of the great length of the typical streamer, the streamer may not travel entirely in a straight line behind the survey vessel at every point along its length due to interaction of the streamer with the water and currents in the water, among other factors.
U.S. Pat. No. 7,221,619 issued to George and commonly owned with the present invention describes a system for controlling deployment and operation of seismic streamers using strain gauges or other tension measuring devices distributed in certain parts of the towing equipment. The measurements from such gauges are used, for example, to determine whether the array of streamers is evenly deployed, whether excessive tension has been experienced by one or more lines or cables, and when a cable should be removed from service.
There exists a need for additional management of tension distribution throughout a marine geophysical survey array to improve operation during surveying and maneuvering, and to optimize efficiency of survey operations.